Related Concept Videos
01:31Energy Stored In A Coaxial Cable
A coaxial cable consists of a central copper conductor used for transmitting signals, followed by an insulator shield, a metallic braided mesh that prevents signal interference, and a plastic layer that encases the entire assembly.
In the simplest form, a coaxial cable can be represented by two long hollow concentric cylinders in which the current flows in opposite directions. The magnetic field inside and outside the coaxial cable is determined by using Ampère's law. The magnetic field inside...
In the simplest form, a coaxial cable can be represented by two long hollow concentric cylinders in which the current flows in opposite directions. The magnetic field inside and outside the coaxial cable is determined by using Ampère's law. The magnetic field inside...
01:18Magnetic Field Due to Two Straight Wires
Consider two parallel straight wires carrying a current of 10 A and 20 A in the same direction and separated by a distance of 20 cm. Calculate the magnetic field at a point "P2", midway between the wires. Also, evaluate the magnetic field when the direction of the current is reversed in the second wire.
01:27Magnetic Field Due To A Thin Straight Wire
Consider an infinitely long straight wire carrying a current I. The magnetic field at point P at a distance a from the origin can be calculated using the Biot-Savart law.
01:28Standing Waves in a Cavity
A household microwave and lasers are examples of standing electromagnetic waves in a cavity. When two conducting metal plates are placed parallel at the nodal planes, it creates a cavity where standing waves are formed. The cavity between the two planes is analogous to a stretched string held at the points x = 0 and x = L. Here, the distance 'L' between the two planes must be an integer multiple of half of the wavelength. The wavelengths that satisfy this condition are given by:
01:27Thermal expansion and Thermal stress: Problem Solving
San Francisco's Golden Gate Bridge is exposed to temperatures ranging from -15 °C to 40 °C. At its coldest, the main span of the bridge is 1275 m long. Assuming that the bridge is made entirely of steel, what is the change in its length between these temperatures?
To solve the problem, first, identify the known and unknown quantities. The initial length (L) of the bridge is 1275 m, the coefficient of linear expansion (α) for steel is 12 x 10-6/°C, and the change in temperature (ΔT) is 55 °C.
To solve the problem, first, identify the known and unknown quantities. The initial length (L) of the bridge is 1275 m, the coefficient of linear expansion (α) for steel is 12 x 10-6/°C, and the change in temperature (ΔT) is 55 °C.
01:22Magnetic Force On Current-Carrying Wires: Example
In a magnetic field, moving charges encounter a force. If a wire contains these moving charges, i.e., if the wire is carrying a current, then a force acts on the wire as well. Consider a pair of flexible leads holding a wire that is 40 cm long and 10 g in weight in a horizontal position. The wire is placed in a constant magnetic field of 0.40 T, as shown in Figure 1(a). Determine the magnitude and direction of the current flowing in the wire needed to remove the tension in the supporting leads.
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Reflection Coefficients for Wires and Cables at 106 mum.
Applied Optics
|February 4, 2010
Summary
This study measured wire reflectivity using a 10.6 micrometer laser, finding high reflectivity for aluminum and lower for hemp rope. Results suggest a low-power laser system for aircraft wire detection.
Area of Science:
- Optics and Photonics
- Materials Science
- Aviation Safety
Background:
- Wire and cable detection is crucial for aviation safety, especially for low-flying aircraft like helicopters.
- Existing detection methods may lack the sensitivity or efficiency required for real-time threat assessment.
- Infrared laser reflectivity of various materials provides insight into potential detection mechanisms.
Purpose of the Study:
- To measure the reflectivity coefficient of diverse wires and cables at 10.6 micrometer wavelength.
- To investigate the influence of polarization (parallel and perpendicular) and incidence angle on reflectivity.
- To assess the feasibility of a laser-based wire avoidance system for aircraft.
Main Methods:
- Experimental measurement of reflectivity coefficients for various wire and cable samples.
Main Results:
- Normal incidence reflectivity varied significantly, from 610% for aluminum wire to 16.8% for hemp rope in parallel polarization.
- Perpendicular polarization reflectivity was consistently lower, reduced by factors of 5.9 to 2.04.
- Depolarization ratios ranged from 17.7% to 1%, increasing with sample irregularity.
- Estimated power requirement for a scanning laser wire avoidance system is low (28 W for a 20°x90° field in 1 sec).
Conclusions:
- The significant reflectivity differences and depolarization characteristics of wires at 10.6 micrometers are quantifiable.
- A scanning laser system with a coherent receiver is a viable concept for aircraft wire detection.
- The low estimated power requirement makes such a system practical for airborne applications, enhancing aviation safety.